During the coming year we will complete the studies of the effect of azide on transforming DNA and on T4 phage. To define specificity of azide mutagenesis, reversion experiments with characterized tryp-E. coli mutants and characterized T4 rII mutants will be performed. To differentiate the effect of azide on metabolizing vs. nonmetabolizing systems, azide mutagenicity will be investigated in mature and replicating phage.